Lysophosphatidic acid (LPA) is a bioactive phospholipid that stimulates cell proliferation, migration, and survival. Five G-protein-coupled receptors have been identified as specific for LPA. Aberrant LPA production, expression, and signalling have been linked to cancer initiation (e.g., tumorigenesis), progression, angiogenesis, and metastasis. LPA is thought to play a role in a number of cancers, including ovarian cancer and other gynecological cancers. LPA also has been linked to cardiovascular disease (e.g., atherosclerosis, atherothrombosis), platelet aggregation, ischemia perfusion injury, wound healing, neuropathic pain, neuropsychiatric disorders, reproductive disorders, and fibrosis.
In recent years, LPA has been considered as an important and sensitive biomarker of ovarian cancer. Elevated LPA levels in plasma have been found in patients with ovarian cancer. There is evidence suggesting that only certain LPA species (below) are associated with ovarian cancer (Sutphen et al., Cancer Epidemiol. Biomark. Prev., 2004, 13:1185-1191; Xu et al. JAMA, 1998, 280:719-732), therefore, quantification of individual LPA species would provide a better way to improve the accuracy of diagnosis. A need also exists for a colorimetric or fluorometric probe capable of detecting equal concentrations of individual LPAs with the same degree of response to more accurately determine total LPA concentration with a single probe.

Known methods suffer from disadvantages. Xu et al. (JAMA, 1998, 280:719-723) used a gas chromatography (GC) method to quantify total LPA plasma levels. Chen et al. (J. Chromatogr. B. Biomed. Sci. Appl., 2001, 753:355-363) used capillary electrophoresis (CE) to quantify individual LPAs with an indirect ultraviolet (UV) for the detection. However, to separate LPA from other lipids before the detection, these and several other studies rely on two-dimensional thin layer chromatography (TLC) as a step, which is time consuming and labor intensive.
Holland et al. (J. Lipid Res., 2003, 44:854-858) used high performance liquid chromatography (HPLC) to separate LPA species and evaporative light-scattering detection (ELSD). This method avoids the two-dimensional TLC step, but LPA elutes at 38 min with a relatively low recovery. LC-MS based methodology has been used to quantify LPAs (Baker et al., Anal. Biochem., 2001, 292:287-295); however, it is not as accurate as LC-MS/MS because LC-MS only determines LPA by detecting the molecular mass ion rather than the parent to daughter ion transitions.
According to some recent studies, LC-MS/MS methods have disadvantages. Shan et al. (J. Chomatogr. B, 2008, 864:22-28) found that some unknown compounds in plasma, which produced the same parent-to-daughter ion transition as LPA in a direct flow injection LC-ESI-MS/MS method, could reduce the accuracy of quantification of LPA. Zhao et al. (J. Lipid Res., 2010, 51:652-659) reported lysophosphatidylcholine (LPC) and lysophosphatidylserine (LPS) could lose the choline or serine group to generate LPA-like signals at the ion source. Additionally, phosphatidic acids may be fragmented by enzymes during separation from blood samples and/or fragmented in an ESI detector, in some instances losing one lipid chain and producing a false positive by appearing as LPA. Another disadvantage is that LPAs do not ionize well, and the best results for LPA typically are obtained by running the mass spectrometer in negative ion mode, which can be more technically challenging than the more typical positive ion mode.